chrome/browser/resources/pdf/elements/viewer-page-indicator/viewer-page-indicator.js

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

Polymer('viewer-page-indicator', {
  label: '1',
  index: 0,
  timerId: undefined,
  pageLabels: null,
  ready: function() {
    var callback = this.fadeIn.bind(this, 2000);
    window.addEventListener('scroll', function() {
      requestAnimationFrame(callback);
    });
  },
  initialFadeIn: function() {
    this.fadeIn(6000);
  },
  fadeIn: function(displayTime) {
    var percent = window.scrollY /
        (document.body.scrollHeight -
         document.documentElement.clientHeight);
    this.style.top = percent *
        (document.documentElement.clientHeight - this.offsetHeight) + 'px';
    this.style.opacity = 1;
    clearTimeout(this.timerId);

    this.timerId = setTimeout(function() {
      this.style.opacity = 0;
      this.timerId = undefined;
    }.bind(this), displayTime);
  },
  pageLabelsChanged: function() {
    this.indexChanged();
  },
  indexChanged: function() {
    if (this.pageLabels)
      this.label = this.pageLabels[this.index];
    else
      this.label = String(this.index + 1);
  }
});